1. Field of the Invention
The present invention relates to a secondary battery apparatus having a secondary battery and a charge controller, and more particularly to a secondary battery apparatus which can reliably charge a secondary battery to a fully charged state for a short time in any environment in which a charge current and an ambient temperature may vary.
2. Background Art
Some electronic devices such as a notebook-size personal computer and so on contain a secondary battery apparatus. This type of secondary battery apparatus includes a secondary battery comprised of a lithium ion battery, a Ni--Cd battery, a Ni--MH battery or the like. The secondary battery functions as a driving power supply when an electronic device is used in an environment in which the electronic device cannot be connected to an external power supply, for example, a commercial power supply. When the battery voltage is reduced as the secondary battery is being used, the secondary battery is charged using a charge power supply (for example, a power supply unit of an electronic device connected to a commercial power supply). The charging of the secondary battery, however, is likely to degrade the battery performance and safety unless the charging is properly carried out.
Thus, the secondary battery apparatus comprises a charge control function for controlling the charging of the secondary battery such that the charging is properly carried out. For example, the charge control function controls the charging such that the secondary battery is charged with a constant current in an initial charge period in which the battery voltage is lower, and is charged with a constant voltage after a predetermined battery voltage has been reached. However, such a constant current/constant voltage charging technique causes a large amount of heat to be generated from a charge power supply, and requires a large charge power supply, thereby causing difficulties in responding to the need for a reduction in size and weight of electronic devices and suppression of the amount of generated heat.
Another charge control technique charges a secondary battery with a constant current while monitoring a battery temperature, taking advantage of the fact that the battery temperature rises as the secondary battery is being charged more. This charge control technique, however, may be affected by an ambient temperature to result in over charging or insufficient charging. In addition, the battery temperature rises due to the heat generated inside the secondary battery, resulting from the continuous charging with a constant current, possibly leading to degraded battery performance.
Also, when a charge power supply for use in charging a secondary battery of a secondary battery apparatus is utilized as a driving power supply for an electronic device, the operation of the electronic device (for example, a hard disk drive built in the electronic device) during a charging process may cause variations in load of the charge power supply to adversely affect the operation of the electronic device as well as the charging of the secondary battery. For example, when the charge power supply has a small size power supply capacity, the operation of the electronic device will become unstable. Also, the charge current may vary with the operation of the electronic device, and a contact resistance at a connector connecting the electronic device with the secondary battery apparatus may vary due to mechanical vibrations caused by the operation of the electronic device. Such variations in the charge current and contact resistance may result in insufficient charging of the secondary battery.